1. Field of the Invention
The present invention relates to interior trim panels for aircraft and, more specifically, to an acoustic absorption trim panel that reduces aircraft interior noise levels.
2. Description of the Prior Art
Acoustical considerations in aircraft design are becoming increasingly important for high-end private aircraft and helicopters. Cabin noise in aircraft can lead to substantial discomfort among passengers and can interfere with aircraft operations. External noise typically comes from the engines, moving parts associated with aircraft components and airflow over the airframe.
Most aircraft are built about a structural framework. An outer skin is applied to the framework and thermal insulation is placed between the skin and the cabin interior. A trim panel, which often has a decorative interior surface, is used to cover the insulation and the framework.
Existing trim panels are typically constructed of a thin layer of a rigid material that has an impact resistance that meets the manufacturer's standards. One side of the rigid material layer may include an aesthetic surface and a layer of sound absorptive material may be applied to the other side. The panel is then attached to the structural framework with anti-vibration mounts. However, such trim panels tend to transmit sound in a manner analogous to that of an audio loudspeaker. Essentially, a local source of noise will cause the entire panel to vibrate, thereby radiating sound into the aircraft cabin.
Several different trim panels have been designed in attempt to reduce noise radiation from outside the aircraft. One type of panel includes a honeycomb core layer made of a rigid material to provide the necessary structural strength and a layer of a damping foam material outside of the honeycomb core layer. An aesthetic décor layer material is placed on the cabin side of the honeycomb core. However, because the honeycomb layer is impervious to air, any air pressure fluctuations (corresponding to noise) that impact the honeycomb layer will radiate across the entire honeycomb layer. Thus, although the foam layer will dampen the noise somewhat, the honeycomb layer will act like an audio loudspeaker that radiates noise throughout the inside of the cabin.
Therefore, there is a need for a rigid, lightweight, acoustic absorption trim panel that both dampens exterior noise and transmits local exterior air pressure fluctuations so as not to radiate noise.